Nozzle for a liquid-cooled plasma cutting torch with grooves

ABSTRACT

This application relates to a nozzle ( 3 ) for a liquid-cooled plasma cutting torch, having at least one groove ( 6   a ) which is arranged on an outer wall ( 4 ) of the nozzle ( 3 ) with which the liquid makes contact, is oriented with the direction of its longitudinal axis ( 18 ) approximately perpendicular to the nozzle mid-axis ( 17 ) of the nozzle ( 3 ) and reduces the wall thickness ( 15 ) of the nozzle ( 3 ), at least in this region, and has a groove base ( 12, 13 ) that reaches into the wall thickness ( 15 ), wherein the groove base ( 12, 13 ) of the groove ( 6   a ) is formed so as to be approximately parallel to the contour of the inner wall ( 5 ) of the nozzle ( 3 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims the benefit under 35 U.S.C.§119 and 35 U.S.C. §365 of International Application No.PCT/EP2011/000433, filed Feb. 1, 2011, the disclosure of which isexpressly incorporated herein by reference.

1. FIELD OF THE INVENTION

The subject matter of the invention is a nozzle for a liquid-cooledplasma cutting torch with improved cooling.

2. PRIOR ART

Plasma cutting is a thermal cutting procedure, in which the material ismelted by the plasma jet, and is blown out of the kerf.

Plasma arc cutting is particularly suited for cutting alloyed steels andnonferrous metals. With these materials, the melting temperatures of theresulting oxides are higher than that of the metal itself. For thisreason, autogenic torch cutting is not possible.

With plasma cutting torches a pilot light arc is ignited between thetungsten electrode and the torch nozzle. The gas flowing through thenozzle is ionized thereby, i.e. it becomes electroconductive (plasmagas). By activating the plasma flow, the arc between the electrode andthe workpiece then burns. The thin plasma jet generated in this mannerexits the cooled tapered nozzle with a high energy density.

The molten liquid material is then blown from the kerf by the high exitspeed of the plasma gas resulting from the uniform advancement of thecutting torch. The cutting rates, depending on the thickness of thematerial, range between 1 m/min. to 8 m/min.

In order to minimize the resulting environmental impacts such as, e.g.smoke, dust, noise and UV radiation during plasma cutting, a watershielding is implemented during the cutting process.

This may be formed either through a water curtain surrounding the torch,or by cutting in a water bath.

Plasma cutting is distinguished by a good cutting quality and a highcutting speed at comparably low costs. As a result, it is already apermanent production fixture in many industrial fields.

Plasma cutting torches are subdivided into two categories:

-   -   Direct plasma generators: The arc is transferred directly to the        substrate that is to be processed. The anode is located outside        of the plasma generator.    -   Indirect plasma generators: The arc exists only in the plasma        generator—the anode is a component of the plasma generator.

With the use of nitrogen, preferably a tungsten electrode is used. Incontrast to this, when compressed air is used, an electrode having azirconium or hafnium coating is used, as said coating results in aformation of a more stable arc spot.

The nozzle of the plasma cutter is exposed to a high thermal load, andfor this reason it is preferably made of a metallic material having ahigh degree of thermal conductivity and electric conductivity as well.In order to obtain greater durability with regard to the nozzle, saidnozzle is cooled with a liquid, such as water, for example. The coolingagent flows through the coolant space formed by the nozzle and thenozzle hood. In order to efficiently exploit the cooling effect of theliquid, according to the prior art, the nozzle has projections extendingfrom the nozzle wall, which are supposed to cause a turbulence in thecooling fluid. This enables a better heat transfer from the nozzle wallto the cooling fluid.

DE 1 565 638 shows a nozzle configuration for a plasma torch. The torchhead has a particularly slender shape and is preferably used for plasmacutting or for the preparation of welding edges. A coolant space isformed between the nozzle hood and the cutting nozzle, designed as astraight, uniform annular channel. The feeding and drainage of thecooling fluid is carried out in the upper region of the torch nozzle.

A nozzle for a liquid cooled plasma torch is described in DE 10 2008 018530 A1. The nozzle features at least one cone-shaped projection on theexterior wall of the nozzle, expanding toward the tip of the nozzle,which forms a flow resistance, or a turbulence, respectively, in thecooling fluid. The projections extend, in all of the embodiment examplespresented therein, away from the exterior wall of the nozzle, and are ata certain angle with respect to the tip of the nozzle.

A plasma torch is described in WO 92/00658 having a nozzle exterior wallwith grooves directed inwards. The incisions are rectangular, and have astraight groove base. The groove base runs parallel to the central axisof the nozzle as a result. In the sloped section of the exterior wall ofthe nozzle, the straight groove base depicts either a cross-sectionreduction of the wall thickness, wherein the wall thickness in the upperregion of the groove base is disadvantageously thin. Or the spacingbetween the interior wall and the straight groove base is so great thatno effective heat transfer from the nozzle wall to the cooling fluid cantake place.

All of the aforementioned embodiments have either a straight coolantspace, or a coolant space having extending projections, respectively, orthey have grooves directed inward having a straight groove base. Bothembodiments present a disadvantage with respect to an efficient heattransfer from the nozzle wall to the cooling fluid.

3. SUBJECT MATTER OF THE INVENTION

The invention therefore assumes the objective of obtaining a nozzle fora liquid cooled plasma torch having an improved cooling effect.

To attain the assumed objective, the invention is characterized by thetechnical teachings of Claim 1.

The substantial characteristic of the invention is that the groove baseof the groove is designed to be substantially parallel to the shape ofthe interior wall of the nozzle.

In a first embodiment, the nozzle has individual grooves, designed asinward oriented incisions in the exterior wall of the nozzle. Thegrooves have preferably a rectangular profile, whereby they have asloped groove base. The sloped groove base is designed such that it runsparallel to the contour of the interior wall of the nozzle. Thisrepresents a substantial advantage over the prior art, because as aresult, a more effective heat transfer from the interior wall to thecooling fluid flowing over the exterior wall can be achieved. In anotherdesign, the grooves can have a trapezoidal profile. In this case, thegrooves become wider in the form of a wedge from the groove baseoutward.

Another advantage is the uniform wall thickness obtained in the regionof the sloped groove base. By this means, not only is a certain minimumwall thickness provided, but at the same time, a good heat transfer isalso ensured.

The number of grooves on the exterior wall of the nozzle should not berestricted to one—numerous grooves in both the straight region as wellas in the sloped region of the nozzle may be present. A symmetricalconfiguration, however, of the annular grooves is preferred.

In a second embodiment the groove is designed as an annular groove, andhas a sloped groove base running parallel to the contour of the interiorwall. A more effective heat transfer over the entire exteriorcircumference of the nozzle takes place by means of the annular groove.

Another advantage is that the sloped groove base enables a minimal wallthickness. Moreover, as a result of the existing minimal wall thickness,an embodiment having numerous annular grooves on the exterior wall ofthe nozzle can be realized.

In another preferred embodiment the groove is designed as a longitudinalgroove, and runs in the direction of the longitudinal central axis ofthe nozzle. By this means, it is possible to allow the cooling fluid torun along the nozzle. The longitudinal groove is preferably rectangularin shape, whereby the groove base is adapted to the contour of theinterior wall. As a result, a good heat transfer is made possible with auniform wall thickness. The embodiment is not limited to onelongitudinal groove thereby; it may also have numerous longitudinalgrooves in an arbitrary configuration on the exterior circumference.

In the following, the invention shall be explained in greater detail,based on drawings depicting only one means of execution. Othercharacteristics and advantages substantial to the invention can bederived from the drawings and the descriptions thereof.

They show:

FIG. 1 a: shows the prior art

FIG. 1: is a schematic depiction of a nozzle having grooves and a slopedgroove base

FIG. 2: is a cut through FIG. 1 having a groove and a sloped groove base

FIG. 3: is a schematic depiction of a nozzle having annular grooves

FIG. 4: is a cut through FIG. 2 having an annular groove and a slopedgroove base

FIG. 5: is a schematic depiction of a nozzle with longitudinal grooves

FIG. 6: is a cut through FIG. 5, with a depiction of the longitudinalgrooves

FIG. 7: is another cut through FIG. 5, with a depiction of thelongitudinal grooves

FIG. 1 a shows the prior art for plasma cutting torch nozzles. Thenozzle device of the plasma torch head 1 consists substantially of anozzle hood 2 and a nozzle 3. A coolant space 10 is formed between thenozzle hood 2 and the exterior wall 4 of the nozzle 3. A cooling fluid,such as water, for example, flows through the coolant space 10, wherebythe liquid is introduced to the coolant space 10 by means of the coolantfeed, and removed by means of the coolant return.

The exterior wall 4 of the nozzle 3 has numerous grooves 6 a havingrectangular profiles, wherein the groove base 12 is straight. Thegrooves 6 a are each directed inward along the longitudinal axis 18 andare at a right angle 19 to the central axis 17 of the nozzle.

The interior wall 5 of the nozzle 3 forms an annular interior spaceabout the central axis 17 of the nozzle for the plasma gas feed 11.

FIG. 1 shows a schematic depiction of a nozzle 3 having numerous,parallel configured grooves 6 a. The grooves 6 a have a largelyrectangular profile, and are located on the exterior wall 4 of thenozzle 3. For this, the embodiment of the groove should not be limitedto a rectangle; any other geometric shape is also possible. The grooves6 a are longitudinal incisions in the exterior wall 4, directed inwardtoward the central axis 17 of the nozzle, wherein the groove base 13 issloped. The slope of the groove base 13 is the result of the angle 14.The angle 14 is the angle to the central axis 17 of the nozzle. Thesloped groove base 13 represents thereby a parallel to the contour ofthe interior wall 5 of the nozzle 3.

With this embodiment, a uniform wall thickness 15 in the region of theincisions is ensured by the grooves. The grooves 6 a are disposed in theconical section of the nozzle 3. Other, additional grooves 23 can bedisposed in the cylindrical section of the nozzle 3, outside of theconical section. These too can exhibit a sloped groove base, as isindicated in FIG. 1. Likewise, this groove base may be designed to bestraight, and parallel to the likewise vertical inner contour there.

As a result of the sloped groove base 13, the cooling fluid can moreeffectively accommodate and discharge heat accumulating on the interiorwall 5 of the nozzle, because the wall thickness is effectivelyminimized and there is no danger that with the creation of the groovesby means of a machining of the tool, the minimized wall will bepenetrated in the direction of the interior circumference of the nozzle.The sloped groove base therefore provides for a uniform, consistent wallthickness 15 at this cross-section of the wall. This was previously notpossible according to the prior art, because the grooves had a straightgroove base 12, and therefore resulted in a varying wall thickness. As aresult, in the region of the groove base, there was a greater and alesser wall thickness, impeding the heat transference.

The embodiment example of FIG. 1 shows a plurality of parallelconfigured grooves 6 a in the conical section of the nozzle 3. These aredesigned either as encompassing or non-encompassing and recessed annulargrooves. Moreover, there is a groove 23 located in the cylindrical,straight section of the nozzle, which can exhibit both a sloped groovebase 13, as well as a straight groove base 12.

FIG. 2 shows a cut through the section indicated in FIG. 1. In thiscase, it concerns a depiction of a nozzle having four recessed grooves 6a, which are evenly distributed on the exterior wall 4 of the nozzle 3,and divided by discontinuation sections 20. In addition, the annularinterior wall 5 of the nozzle 3 is depicted, which serves as the plasmagas feed 11.

A nozzle is shown in FIG. 3, having a plurality of annular grooves 6 bon the exterior wall 4 of the nozzle 3. The annular grooves 6 b have astraight groove base 12 in the upper, cylindrical section 21, and in thelower, conical section 22, they have a sloped groove base. The positionsof the respective groove bases (12, 13) are based on the contour of theinterior wall, and always run parallel thereto. Moreover, it is visiblein this depiction that the wall thickness 15 remains constant in allregions of the grooves 6 b. This enables an effective heat transfer fromthe interior wall 5 of the nozzle 3 to the cooling fluid.

FIG. 4 shows a cut through the region indicated in FIG. 3. This shows atop view of the nozzle 3 with the individual wall thicknesses and theencompassing annular groove 6 b. The innermost ring forms the interiorwall 5 of the nozzle 3, followed by the encompassing annular groove 6 band the exterior wall 4 of the nozzle 3. In addition, the largestcircumference of the exterior wall 4 of the nozzle is depictedschematically. The encompassing annular groove 6 b can likewise bedivided by differently sized discontinuation regions 20.

A nozzle 3 having longitudinal grooves 16 is depicted in FIG. 5. Thesepreferably have a rectangular cross-section and run along thelongitudinal axis in the exterior wall 4 of the nozzle 3. Therectangular cross-section is only to be regarded in this case asexemplary; any other geometric shape is also possible for the groove.Likewise, it is possible that the longitudinal grooves 16 only bepresent in the upper, cylindrical section 21 or in the lower, conicalsection 22.

FIG. 6 shows a first cut through the FIG. 5. The longitudinal grooves 16are located in the exterior wall 4 of the nozzle 3. The wall thicknessis, however, reduced to the same degree in all regions of the grooves.The interior wall 5 of the nozzle 3 is designed to be annular in shape,and serves to conduct plasma.

FIG. 7 shows another cut through FIG. 5. The longitudinal groove 16extends thereby along the body of the nozzle, both over the cylindricalsection 21 as well as over the conical section 22, and is located in theexterior wall 4 of the nozzle 3.

The invention also claims a configuration, or combination, respectively,in which both annular grooves 6 a, 6 b as well as longitudinal grooves16, 22 are disposed.

KEY TO THE DRAWINGS

-   1. plasma torch head-   2. nozzle hood-   3. nozzle-   4. exterior wall (nozzle)-   5. interior wall (nozzle)-   6 a. groove (incision)-   6 b. annular groove-   7. projection-   8. cooling agent feed-   9. cooling agent return-   10. coolant space-   11. plasma gas conductor-   12. groove base (straight)-   13. groove base (sloped)-   14. angle-   15. nozzle wall (wall thickness)-   16. longitudinal groove-   17. central axis of the nozzle-   18. longitudinal axis-   19. angle-   20. discontinuation section-   21. region-   22. region-   23. groove (straight region)

The invention claimed is:
 1. A nozzle for a liquid-cooled plasma cuttingtorch, comprising: a plurality of closed, spaced annular groovesdisposed on a tapered exterior wall of the nozzle that comes intocontact with a liquid, the annular grooves having a longitudinal axissubstantially perpendicular to a central axis of the nozzle, wherein theannular grooves reduce a thickness of the exterior wall of the nozzle inat least this region, and each annular groove having a groove baseextending into the wall, wherein the groove bases of the annular groovesare substantially parallel to a contour of an interior wall of thenozzle; a plurality of discontinuous portions of the exterior wall beingspaced apart from each other by at least one of the annular grooves; anda plurality of longitudinal grooves extending along a longitudinallength of the exterior wall, each longitudinal groove having a regionhaving a straight groove base and a region having a sloped groove baseat an angle to the central axis of the nozzle, at least one of thestraight groove base and the sloped groove base of each of thelongitudinal grooves being substantially parallel to the contour of theinterior wall of the nozzle.
 2. The nozzle according to claim 1, whereinthe thickness of the wall is reduced to the same degree in the region ofthe groove base of the annular grooves.
 3. The nozzle according to claim1, wherein each of the annular grooves is a closed, annular grooverunning along a circumference of the nozzle.
 4. The nozzle according toclaim 1, wherein each of the annular grooves is positioned on acircumference of the nozzle and is spaced apart from adjacent annulargrooves by at least one of the discontinuous portions of the exteriorwall.
 5. The nozzle according to claim 1, wherein the longitudinalgrooves run in the exterior wall of the nozzle.
 6. The nozzle accordingto claim 2, wherein each of the annular grooves is a closed, annulargroove running along a circumference of the nozzle.
 7. The nozzleaccording to claim 3, wherein each of the annular grooves is positionedon a circumference of the nozzle and is spaced apart from adjacentannular grooves by at least one of the discontinuous portions of theexterior wall.
 8. The nozzle according to claim 2, at least one whereinthe longitudinal grooves run in the exterior wall of the nozzle.
 9. Thenozzle according to claim 3, wherein the longitudinal grooves run in theexterior wall of the nozzle.
 10. The nozzle according to claim 4,wherein the longitudinal grooves run in the exterior wall of the nozzle.11. The nozzle according to claim 2, wherein the other of the slopedgroove base and the straight groove base of each longitudinal grooveruns substantially parallel to the contour of the interior wall of thenozzle.
 12. The nozzle according to claim 3, wherein the other of thesloped groove base and the straight groove base of each longitudinalgroove runs substantially parallel to the contour of the interior wallof the nozzle.
 13. The nozzle according to claim 4, wherein the other ofthe sloped groove base and the straight groove base of each longitudinalgroove runs substantially parallel to the contour of the interior wallof the nozzle.
 14. The nozzle according to claim 5, wherein the other ofthe sloped groove base and the straight groove base of each longitudinalgroove runs substantially parallel to the contour of the interior wallof the nozzle.
 15. A nozzle for a liquid-cooled plasma cutting torch,comprising: a plurality of spaced annular grooves disposed on anexterior wall of the nozzle that comes into contact with a liquid, eachof the annular grooves having a longitudinal axis substantiallyperpendicular to a central axis of the nozzle, wherein the annulargrooves reduce a thickness of the exterior wall of the nozzle in atleast this region, and each annular groove having a groove baseextending into the wall, wherein the groove bases of the annular groovesare substantially parallel to a contour of an interior wall of thenozzle.
 16. The nozzle of claim 15, further comprising a plurality ofdiscontinuous portions of the exterior wall spaced apart from each otherby at least one of the annular grooves.
 17. The nozzle of claim 15,wherein each of the annular grooves is a closed, annular groove runningalong a circumference of the nozzle.
 18. A nozzle for a liquid-cooledplasma cutting torch, comprising: a plurality of longitudinal groovesextending along a longitudinal length of the nozzle, each longitudinalgroove having a region with a straight groove base and a region with asloped groove base at an angle to the central axis of the nozzle, and atleast one of the straight groove base and the sloped groove base of eachof the longitudinal grooves is substantially parallel to the contour ofthe interior wall of the nozzle.
 19. The nozzle of claim 18, furthercomprising a plurality of discontinuous portions of the exterior wallspaced apart from each other by at least one of the longitudinalgrooves.
 20. The nozzle of claim 18, wherein the other of the slopedgroove base and the straight groove base of each longitudinal grooveruns substantially parallel to the contour of the interior wall of thenozzle.